Thanks for doing the research. I'm new to all this and trying to find answers...
I don't take it, but I did find this while doing a bit of research:
Adverse Effects
Some people in the clinical trials reported mild digestive upset.
There are no other reports of side effects, although increased thyroid gland activity could presumably lead to complications such as nervousness, weakness, palpitations, or eye problems.
Possible Interactions
No drug interactions have been reported.
In theory, guggul might counteract thyroid-suppressing drugs or increase the effect of thyroid hormones such as Synthroid or Levoxyl. Monitoring of thyroid function is prudent.